The Los Alamos National Laboratory (“LANL”) currently uses about 1100 acre-feet per year of water in cooling towers. Approximately 50% of this water is returned to the environment as blowdown (i.e. discharged water) that contains antibacterial and antiscaling chemical additives as well as concentrated natural solutes. Chemical costs are about $1011000 gallons. An NPDES permit is required for discharge of the water from these towers.
Cooling towers at LANL use potable water from a regional aquifer that contains between 60 to 100 mg/L of silicon-containing species that include silicic acid, silicates, polysilicic acid species, and other silicon containing species that have been expressed collectively as silica. Because the solubility of silica is approximately 160 mg/L, cooling towers must operate at less than 2 cycles of concentration (“COC”). With antiscaling additives, the towers can be operated up to about 2.5 cycles of concentration (<200 mg/L). Removal of silica from cooling tower makeup water or in situ concentrated cooling tower water would increase the potential COC, and thus reduce the need for makeup water and blowdown discharge. Considerable cost savings would be realized if even a fraction of the existing silica could be removed.
Theoretical calculations by Midkiff in U.S. Pat. No. 6,416,672 indicate that a treatment system containing glass beads would be successful in removing both dissolved and colloidal silica from cooling tower water if a sufficient quantity of small glass beads were used to overwhelm the surface area of the system by a factor of 100 or more. If it worked well, treatment using glass beads according to Midkiff appeared to be a solution to the LANL problem of removing silica from cooling tower water. If not, then there remains a need to reduce the amount of silica in concentrated cooling tower water and makeup water at Los Alamos National Laboratory (“LANL”), and at other places where high silica concentration cooling water is used, such as other heat exchange systems. There is also a need to control costs associated with antiscaling chemical use and discharged water (“blowdown”) treatment, and to reduce the need for makeup water addition.